5.2. Performance comparison between R410A and R32 with vapor injection
Experimental tests with vapor injection were also conducted. In this operation mode the heat pump system works as a two stage cycle. During the experiments the upper stage expansion valve was controlled to vary the injection pressure, which results in different injection ratios. The vapor injection system performance was compared with non-injection performance to investigate the system performance improvement at different injection ratios. Fig. 9 shows the vapor injection capacity improvement for R32 and R410A. In the heating mode as shown in Fig. 9a, the capacity improvement was observed to be significant. Maximum capacity improvement was observed at the lowest ambient temperature of "18 #C. Capacity improvement for R410A and R32 was observed to be 33% and 25%, respectively. The capacity improvement also increases with the injection ratio. It should be noted that the maximum injection ratio is limited by the amount of vapor available in the flash tank, and also limited by the liquid level in the flash tank. Increasing the opening of the upper-stage expansion valve leads to a higher injection pressure, and therefore, increases the injection ratio. However, the liquid level in the flash tank is also increased as the upper stage expansion valve’s opening increases. Fig. 9b shows the capacity comparison between R32 and R410A for the cooling mode. The maximum capacity improvement for R410A was observed to be 18%, and the maximum improvement for R32 was only 4%. As the injection ratio increases, the improvement remains almost the same. The main reason is that vapor injection has larger impact on the condenser than on the evaporator, and therefore the benefits in heating mode are more than in cooling mode.